The present invention relates to thermostats and more particularly to thermostats used in cooling systems of internal combustion engines
Thermostats are commonly used to enable liquid-cooled automotive and industrial engines to operate within their specified design temperatures. When an engine is started, the thermostat operates to trap water within the engine, thereby enabling the engine temperature to increase. Once the operating temperature has been reached, the thermostat operates to permit the coolant to flow to a radiator. The coolant transfers heat from the engine to the radiator, thereby cooling the engine and preventing it from exceeding a maximum allowable operating temperature. Thus, by regulating the flow of coolant from the engine block to the radiator, the thermostat compensates for variations in load and ambient temperature and thereby maintains the temperature of the engine within an allowable operating range. Among the known thermostats, two types of valves are commonly used. The first type of valve, such as the one disclosed in U.S. Pat. No. 2,777,638, issued to C. W. Wood on Jan. 15, 1957, has a rectilinear movement. The second type of valve, such as the one disclosed in U.S. Pat. No. 2,815,174, issued to V. E. Rimsha on Dec. 3, 1957, is a butterfly type which swings about a transverse axis. Both types of valves are designed to operate between a closed position in which water is trapped within the engine and an open position in which water is allowed to flow from the engine to the radiator. When either valve is in the closed position, it rests upon a seat member which limits motion in the closing direction. Once the engine reaches its operating temperature, a temperature-responsive material contained within a plunger expands and thereby moves the valve to its open position.
As with any mechanical device, valves are subject to failure. If a valve fails to open, the coolant is trapped inside the engine and cannot transfer heat to the radiator; therefore, the engine temperature rises beyond the maximum allowable operating temperature, resulting in heat damage which can range from cylinder head gasket failure, to a cracked cylinder head or engine block, to a seized engine. Thus, a defective thermostat can cause catastrophic engine damage.
The prior art is aware of a need to guard against thermostat malfunctions. For example, U.S. Pat. No. 2,769,597 issued to E. L. Mayo on Nov. 6, 1956 discloses a thermostat that guards against valve failure due to the loss of expansible material An expansion member containing the expansible material is connected to the valve by a diaphragm and linkage element. As the material is lost, the diaphragm and linkage element move the valve to the open position. Thus, even though the expansion member cannot move the valve, the valve is still partially open position, thereby allowing water to flow therethrough. While this device safeguards against a loss of expansible material, it does not guard against situations where the valve sticks to the seat.
Therefore, it is an object of the present invention to provide an improved thermostat having a means for bypassing the valve in the event the valve fails to open.
It is a further object of the present invention to partially construct the improved thermostat from a material that melts when the engine exceeds its maximum operating temperature, thereby providing a passage for the coolant to bypass the valve.